A scheme paying farmers in Wales to protect the environment has brought benefits but has cost more to run than anticipated, a report has found.
Lapwing is one species helped by practices encouraged by Tir Gofal
Tir Gofal pays farmers to use their land less intensively, and let some sections become havens for wildlife.
Since 1999, it has paid landowners about £100m and created 112 jobs.
The Wales Audit Office (WAO) says Tir Gofal is working, but it must be more flexible and needs money to continue in the long term if it is to be a success.
In return for payments under the scheme, landowners reduce the number of animals grazing their land, leaving strips at the edge of fields for wildlife or helping regenerate hedgerows.
The WAO said the scheme - Tir Gofal is Welsh for "land in care" - now covers 20% of agricultural land in Wales and has proved to be extremely popular with landowners, with a waiting list of applications.
The Countryside Council for Wales ran Tir Gofal from its start until October 2006, when responsibility for its administration was taken over the Welsh Assembly Government.
The assembly government part-funds the payments, which amounted to £20m in 2006-2007.
The report found the scheme had brought additional spending in the local economy, totalling £4.2m, when last measured in 2003.
It said it was too soon to assess the full impact of the scheme, as environmental change can take a very long time and there were significant gaps in the assembly government's research and evaluation criteria.
It also said some farmers and stakeholders had reservations about the flexibility and targeting of the scheme.
Auditor General for Wales Jeremy Colman said: "There are promising signs that the Welsh countryside is benefiting from Tir Gofal, but some changes are needed to ensure that these benefits are sustained.
"Improving the measurement and evaluation of performance and streamlining some aspects of the scheme's design should make Tir Gofal even better equipped for the future."